D-13 Body Mold

[Greg Davis]

I am thinking of trying to make a lighter body for my D-13 and was wondering if anyone might be able to direct me to someone who would have a main body mold for this car.

[fvracer27]

Dave Kazmierczak make 3 piece mid section as well as tails and noses still. Not sure how much lighter you can make it unless it was Carbon but at that point why? I'm only 90lbs over so it's just gonna make me diet. if your under 195 you should not be that far off in a D13 unless you 4" frame tubes are solid

Mark

[Greg Davis]

Mark, Thanks for the info on Dave K. I am currently 25 lbs over, but according to a very good source, for every 10 lbs extra you're carrying around, you're losing 1 HP. I know it's a lot of trouble to go through for a few lbs., but every little bit of advantage adds up, especially in Vee racing (and especially with an older car).

[kpkehoe]

I've got a main body mold I would be happy to let you use but I am in Los Angeles.

[jpetillo]

Mark, Thanks for the info on Dave K. I am currently 25 lbs over, but according to a very good source, for every 10 lbs extra you're carrying around, you're losing 1 HP. I know it's a lot of trouble to go through for a few lbs., but every little bit of advantage adds up, especially in Vee racing (and especially with an older car).

Greg, I don't believe this is true. A 1% change in weight can at best equate to a 1% change in HP, not 2%. And that would only be the case if there were no such thing as wind resistance and frictional losses in the drivetrain. When all is said and done after considering the conditions you're under at a track, you're probably looking at 10 lbs equating to less than a 1/4 HP change.

That being said, you should always try to get to your target weight. If you're 25 lbs over 1025, how far do you plan to bring it down - 10-15 lbs? You will need some margin for variations between scales. John

[fvracer27]

John does that mean I can still eat cheese burgers haha everyone always has told me in the past "your heavier, so you have more grip " skinny guys don't like getting beat by fat guys

Mark

[fvracer27]

Hey Kevin is that a 1 piece mold?

Mark

[jpetillo]

John does that mean I can still eat cheese burgers haha everyone always has told me in the past "your heavier, so you have more grip " skinny guys don't like getting beat by fat guys

Mark

Mark, That's funny. I have to watch what I say because I can only get myself into trouble, here! Less overall weight is always better - no arguing with that. However, judging from the speed of others on the track in our region, there is an amazing lack of correlation between weight and lap times in FV - not that there is none. I'm about 12 lbs over minimum, and I seem to beat no-one out of the corners due to acceleration. I may not have the best engine, but it's probably within spitting range of most others. I believe that some of the national racers have also noted a lack of correlation between their overall weight and lap times. I don't remember what amount of weight difference they were talking about, though. Maybe they will see this thread and respond. What they say can help indicate where to spend one's time in terms of time spent on weight reduction vs. preparation and practicing. When my daughter and I were sharing the car last year and the year before, it was about 40 lbs over my usual setup weight when I drove it, and my times were better than the previous year when it was the right weight. I don't claim that more weight correlates to better lap times, but I couldn't see the change. I expect that better drivers would. John

[Greg Davis]

This has turned into an interesting thread.
My basic line of thought is what extremes professional teams that are dealing with high H P cars will go to to eliminate relatively small amounts of weight to gain an advantage. I think of lifting a 25 lb. sack of anything and carrying it around and that illustrates for me what that 1200 cc VW engine goes through every time it has to accelerate. I am also trying to balance the car and eliminate rear weight biased polar moment. The D-13 has excellent handling already and I am trying to maximize that. In my opinion weight bias helps accentuate (or detract from) that characteristic.
Kevin,
I am going to be out in the Lake Havasu area in January-February and if your offer still holds perhaps we could get together.

[kpkehoe]

Mark,

It's a two piece mold, slit down the middle. I would pick up 20-30 C-clamps from Harbor Freight and assemble it, using filler in the seam. If done with a little care, you will produce a very nice panel. It's been some years since I popped a panel but the process doesn't change. Use fresh materials and send as much time as you can on preparation.


Kevin

[fvracer27]

Mark,

It's a two piece mold, slit down the middle. I would pick up 20-30 C-clamps from Harbor Freight and assemble it, using filler in the seam. If done with a little care, you will produce a very nice panel. It's been some years since I popped a panel but the process doesn't change. Use fresh materials and send as much time as you can on preparation.


Kevin

sorry I ment a mold that will produce a 1 piece mid section I would like to make a 1 piece mid

Mark

[SR Racing]

Mark, Thanks for the info on Dave K. I am currently 25 lbs over, but according to a very good source, for every 10 lbs extra you're carrying around, you're losing 1 HP.).

You can do this problem mathmatically but it has some holes in it.
Here is some results with caveates later:

A 1050lb mass with about 54hp (Vee) to the wheels can accellerate 1000 feet in 10.22 seconds.
A 1050lb mass with about 53hp (Vee) to the wheels can accellerate 1000 feet in 10.17 seconds.
A 1100lb mass with about 52hp (Vee) to the wheels can accellerate 1000 feet in 10.22 seconds.
(Typical drag, air density losses included)

So roughly based upon the math, 50 lbs equals 2 HP. Now for the big caveates: The math has to assume a steady HP. ie,You have the same HP all the way through the accelleration run. Not true. On a Vee from 4500 to 6500RPM you will vary from ~48 to 54hp or so. The above exact numbers could only be achieved with a constant variable transmission (one with little loss). Also your shift points will make a difference.

But... certainly 50lbs on a 53 hp car makes a load of difference. Now we have to throw in the cornering mass and center of gravity issues. 50lbs hurts there also. You can figure those out for yourself.

So Greg, you are losing at least 1HP on the straights and some undetermined cornering capabilty. (Not to mention additional tire wear, and about 25 cents additional in fuel costs per weekend.

Jim

[SR Racing]

My basic line of thought is what extremes professional teams that are dealing with high H P cars will go to to eliminate relatively small amounts of weight to gain an advantage.

Teams are paying $400 extra for the Pro Hans unit simply because it weighs ~ONE pound lighter. The weight is not a comfort issue since the hans is pressed down on the shoulders and the driver can't feel the extra weight. However the car is now 1 lb lighter. I have explained this to some teams that have ordered from us and they totally understand and pay the extra for the PRO unit.

[tiagosantos]

The Pro Hans thing.. Isn't that a question of self image, too? If I was racing in a pro series and had a million bucks in my bank account, I wouldn't want to be seen with a plastic POS around my neck either!

[fvracer27]

$400 for 1lbs is crazy the both function the exact same from what I'm told. $400 can be spent it other places.

Mark

[FV80]

A 1050lb mass with about 54hp (Vee) to the wheels can accellerate 1000 feet in 10.22 seconds.
A 1050lb mass with about 53hp (Vee) to the wheels can accellerate 1000 feet in 10.17 seconds.
A 1100lb mass with about 52hp (Vee) to the wheels can accellerate 1000 feet in 10.22 seconds.
...
Jim

What am I missing, Jim?? Your numbers make NO sense to me. As you posted, a 'mass' @ 1050 lbs can cover 1000 feet in 0.05 seconds *LESS* (i.e. gets there sooner) if he has 1 LESS HP.
Then he can add 50 lb and take away another HP (now @ 52) and still get there in the same amount of time as he did @ 1050 w/54 HP.. ??

I'm lost ... I'm assuming there is/are some typo(s) in your post, but I have no idea where....
... Maybe I just don't understand the term "accellerate 1000 feet" ?? I took it to mean that a "mass" could motivate itself to 1000 feet from a standstill in that amount of time. Did you mean something different?

Steve, FV80

[tiagosantos]

I'm assuming the 54 and 52 are switched

[jpetillo]

You can do this problem mathematically but it has some holes in it.
Here is some results with caveats later:

A 1050lb mass with about 54hp (Vee) to the wheels can accelerate 1000 feet in 10.22 seconds.
A 1050lb mass with about 53hp (Vee) to the wheels can accelerate 1000 feet in 10.17 seconds.
A 1100lb mass with about 52hp (Vee) to the wheels can accelerate 1000 feet in 10.22 seconds.
(Typical drag, air density losses included)
Jim

Jim,
Under a constant 52 HP to the wheels (I assume that you swapped HP between the top and bottom), and with no aero drag at all (or any drag), it takes 10.87 seconds to accelerate 1050 lbs 1000 ft. Adding aero drag would just make this take longer. Even 54 HP is in this same ballpark. I think something's missing from your calculation.

By the way, what are you considering for a Cd*area?

John

[jpetillo]

I did this calculation pretty carefully and included aero forces. I took the case of accelerating from 60 to 94 mph. This is similar to doing the straight at NHMS. The slowest corner - the hairpin - is taken at 40. I think all other corners outside of turn three is at about 60 or more. It's arguable if this is typical of other tracks or not. The point is that we're almost always above 60, so that's where we should look at the effect of added weight.

Like Jim suggested, I chose a constant HP to the rear wheels. I used FV aero drag data. I looked at the time to cover the distance for the first Reference Case and kept distance-covered the same for the other cases.

1050 lbs - 52.0 HP - 1520 ft - 60-94 mph: Reference Case
1050 lbs - 53.0 HP - 1520 ft - 60-94 mph: 0.06 seconds faster

1100 lbs - 53.0 HP - 1520 ft - 60-94 mph: 0.02 seconds SLOWER
1100 lbs - 53.2 HP - 1520 ft - 60-94 mph: 0.01 seconds SLOWER
1100 lbs - 54.0 HP - 1520 ft - 60-94 mph: 0.03 seconds faster
(I edited/corrected some of the numbers. The calculation is only good to 0.01 seconds)

So, we're looking at about 1.2 HP to make up for 50 lbs in this specific case. I had guessed about 1/4 HP for 10 lbs additional before. That's close to this proportion.

We haven't considered the effect of weight on cornering, uphills or downhills, but the above gives some indication of the effect.

I hope this helps. John

[problemchild]

Greg D.
Please check your messages.
Thanks!